Zinc-alkaline batteries represented by alkaline-manganese dry cell batteries are widely used as a power source for various devices, due to its all-purpose application and low costs. In zinc-alkaline batteries, a zinc powder of an indefinite form made by gas atomization is used as the negative electrode active material.
However, corrosion of the zinc powder in the alkaline electrolyte generates hydrogen gas, sometimes causing an increase in the internal pressure of the battery and leakage. Thus, it is important to curb the zinc powder corrosion and improve reliability of zinc-alkaline batteries.
As a measure, for example, mercury is added in the negative electrode to amalgamate the zinc powder surface, to increase the hydrogen overvoltage for improving resistance to corrosion. However, with increasing environmental concerns and no-mercury requirement mainly for alkaline-manganese dry cell batteries around 1980 to 1990, instead of such a measure, for example, following (A) to (C) were proposed. Currently, zinc-alkaline batteries using various combinations of (A) to (C) are examined.
(A) For the negative electrode active material, an excellently corrosion-resistant zinc alloy powder including aluminum, bismuth, or indium is used (for example, Japanese Laid-Open Patent Publication No. Hei 5-166507).
(B) To the negative electrode, an inorganic anticorrosive such as indium hydroxide, bismuth hydroxide, indium sulfide, and a sulfide of an alkaline metal is added (for example, Japanese Laid-Open Patent Publication No. Sho 48-77332, Japanese Patent No. 2808822, and Japanese Patent No. 2754864).
(C) To the negative electrode, an organic anticorrosive such as a surfactant is added (for example, Japanese Laid-Open Patent Publication No. Hei 5-266882).
With recent advancement of digital and higher performance devices, electrical load required for zinc-alkaline batteries such as alkaline-manganese dry cell batteries used as a power source for these devices is increasing. As a measure, for example, Japanese Laid-Open Patent Publication No. 2001-512284 and Japanese Laid-Open Patent Publication No. 2002-270164 have proposed usage of a zinc powder including plenty of micropowder with a particle size of 75 μm or less to pass through a sieve of 200 mesh, as the negative electrode active material, to increase reactivity and to improve discharge performance at high load.
However, when a plurality of the batteries including zinc micropowder as the negative electrode active material were connected in series and discharged with a constant resistance, among the plurality of batteries, the battery with a small capacity is prone to overdischarge, and with a further advancement of the overdischarge, the battery is reverse-charged, and the polarity is reversed in at least one of the positive electrode and the negative electrode, sometimes causing significant leakage. To be specific, when a plurality of alkaline-manganese dry cell batteries are connected in series and used as a power source for a toy or a light, and the batteries are left connected after the usage, there is a possibility of leakage. The device may be damaged by such a leakage.
The gas generation reaction (water decomposition reaction) upon the polarity reverse of the positive electrode and the negative electrode is represented by the formula below. When the amount of the current being passed is the same in the positive electrode and in the negative electrode, the amount of hydrogen gas generated by the polarity reverse in the positive electrode becomes twice the amount of oxygen gas generated by the polarity reverse in the negative electrode. Therefore, at the time of overdischarge, the polarity reverse in the positive electrode generates a greater amount of gas than the polarity reverse in the negative electrode, increasing the battery internal pressure and leakage.
(Polarity Reverse Reaction in Positive Electrode)2H2O+2e−→H2+2OH−(Polarity Reverse Reaction in Negative Electrode)4OH−→O2+2H2O+4e−
Thus, to solve the conventional problems as noted in the above, the present invention aims to provide a zinc-alkaline battery that is excellent in discharge performance at high load, highly reliable, and able to curb leakage from a significant increase in battery internal pressure involved with gas generation at the time of overdischarge, even when a micropowder negative electrode active material is used.